1. Field of the Invention
This invention relates to a valve of the type commonly referred to as a top-entry metal-seated ball valve, as well as to the combination of said valve with an actuator specially adapted for use therewith.
2. Description of the Prior Art
There exists a long felt and heretofore unsatisfied need for a quick-acting low-cost on-off valve having the capability of achieving ANSI (American National Standard Institute) pressure-temperature ratings. Conventional gate valves, with their metal-to-metal seating and wedging action, satisfy many of these requirements. However, because a screw thread is used to force the wedging action, many turns of the operating handle are required to move the wedge between its fully open and fully closed positions. Thus, quick action becomes an impossibility with valves of this type.
Moderately priced 1/4 turn ball valves also achieve many of the above-stated requirements. However, such valves lack the ability to achieve high pressure-temperature ratings because they employ resilient elastomeric seats, whose pressure retaining capabilities drop rapidly as temperatures increase.
Metal-seated ball valves also are available which again achieve many but not all of the above-stated requirements. Because such valves require extremely precise machining and assembly, their costs are extremely high and this in turn severely limits where they can be used.